Retinal amacrine cells are interneurons that help to shape the visual signal that ganglion cells send to other visual centers in the brain. The ultimate goal of the research proposed here is to understand the factors that underlie the dynamics of calcium and calcium dependent signaling within and between amacrine cells. A better understanding of signal processing in the retina will be valuable in helping us to better understand how signals are shaped elsewhere in the brain. This proposal specifically addresses the role of mitochondria in shaping the temporal and spatial properties of calcium signals and calcium-dependent processes in amacrine cells. Mitochondria are especially interesting because they can be a spatially discrete sink and source of calcium. This is relevant to amacrine cell function in particular because it is thought that much of the synaptic signaling in amacrine cells is spatially localized rather than spread over broad regions of the cell. To understand the role of mitochondria in amacrine cell signaling, we propose the following three specific aims: Specific Aim 1: To elucidate the impact of mitochondrial calcium buffering on the spatial and temporal aspects of calcium elevations in amacrine cells. Specific Aim 2: To discover the role of mitochondrial calcium buffering during synaptic transmission between GABAergic amacrine cells. Specific Aim 3: To uncover the interactions between mitochondria and other mechanisms and organelles relevant to calcium signaling in amacrine cells. To achieve these three aims, amacrine cells cultured from the chick retina will be used as a model system for amacrine cells in the intact retina. This system will allow the examination of single amacrine cells or pairs of amacrine cells participating in functional GABAergic synapses, an extremely common type of synapse found in the retina. The proposed research will employ calcium imaging, whole cell voltage clamp recordings, immunocytochemistry and confocal microscopy to achieve the stated aims. These studies will lead to insights into the mechanisms that underlie the processing of the visual signal in the vertebrate retina.